A billion-year arms race against viruses shaped our evolution

By Amy Maxmen

Viruses and their hosts have been at war for more than a billion years. This battle has driven a dramatic diversification of viruses and of host immune responses. Although the earliest antiviral systems have long since vanished, researchers may now have recovered remnants of one of them embedded, like a fossil, in human cells.

A protein called Drosha, which helps to control gene regulation in vertebrates, also tackles viruses, researchers report today in Nature1. They suggest that Drosha and the family of enzymes, called RNAse III, it belongs to were the original virus fighters in a single-celled ancestor of animals and plants. “You can see the footprint of RNAse III in the defence systems through all kingdoms of life,” says Benjamin tenOever, a virologist at Icahn School of Medicine at Mount Sinai in New York and lead author of the paper.

Plants and invertebrates deploy RNAse III proteins in an immune response called RNA interference, or RNAi. When a virus infects a host, the proteins slice the invader’s RNA into chunks that prevent it from spreading. But vertebrates take a different approach, warding off viruses with powerful interferon proteins — while Drosha and a related protein regulate genes in the nucleus.

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